Journal of Structural Engineering

Four beam models were examined in tests of reinforced concrete (RC) columns failing in flexural yielding with ends rotated independent of each other. A one‐component model assuming an elastic member with rigid‐plastic springs at critical sections gave the best prediction, although this model slightly underestimated the nondiagonal terms of the flexibility matrix, which represent the interaction between the two ends of a member. A model connecting many inelastic flexural springs slightly overestimated the nondiagonal terms and the energy dissipation. A composite model and a prescribed flexibility distribution model over‐estimated both the diagonal and nondiagonal terms, resulting in smaller energy dissipation than observed. This tendency was closely related to the crack pattern: the observed crack pattern was between those assumed in the one‐component model and the model connecting many inelastic flexural springs. This conclusion may be extended to RC columns, beams, and multistory structural walls in general as long as they fail in flexural yielding, because their crack patterns are similar to that observed in the writers' tests.

This paper investigates theoretically the effect of bolt slippage on the deflection and ultimate‐strength responses of lattice structures. For the purpose of this study, two idealized bolt‐slippage models are presented. The effect of bolt slippage was incorporated into the previously developed nonlinear finite element computer program, AK TOWER, by Al‐Bermani and Kitipornchai, in 1992. Two lattice structures are used to study the influence of bolt slippage. Results of this study illustrate that while the slippage of bolts may have some effect on deflection, it does not significantly influence the ultimate strength of lattice structures.

The arch is a very common masonry structure that has been studied extensively in the past. Despite this, no analytical methods exist that can adequately evaluate the collapse mechanisms and their related loads. This paper presents a collapse approach that takes into account the small tensile and shear strengths of masonry material according to a no‐tension constitutive model. Some appropriate analytical functions are proposed that can reproduce the collapse mechanisms and the values of the associated horizontal limit thrusts at the arch's skewback. This approach also provides the minimum value for the thickness‐span ratio, the safety margin, and the maximum value of uniformly distributed vertical loads (load parameter). The collapse mechanisms' shapes and the horizontal limit thrusts are then analyzed as a function of the loads and the arch's geometry. In addition, the findings are compared to the results of a finite‐element analysis.

Aspects relating to the shear strength of circular and rectangular columns under seismic loading are presented. An examination of existing design equations reveals wide differences in predicted responses. Particular emphasis is placed on models capable of representing the interaction between flexural ductility and shear strength. A simple method is proposed whereby the strength enhancement provided by axial compression is separated from the concrete component of shear strength and considered to result from arch action. The strength of the concrete component is reduced as flexural displacement ductility increases. Prediction of shear strength from the proposed and alternative methods are compared with results from a wide range of tests of columns failing in shear. The proposed method is shown to provide significantly improved correlation with experimental results. Conservative modifications are made to enable the method to be used for design.

Guidelines are presented for the design of beam‐column moment‐resisting joints in composite framed structures consisting of structural steel beams and reinforced concrete or composite columns. These recommendations address the proportioning and detailing of these joints, taking into account the interaction of the structural steel and reinforced concrete components. The recommendations are based primarily on tests of cruciform‐shaped specimens and on related information from existing codes and standards. The typical joint configuration is one where the steel beams are continuous through the reinforced concrete column. Such connections are increasingly being used in the United States, Japan, and elsewhere. Since many of the concepts are being introduced for the first time, a commentary is provided that identifies additional reference material. Examples are included to demonstrate the use of these design recommendations.

The current approach for seismic retrofit of bridge columns in California involves extensive use of steel jacketing, which has been shown to be very effective in enhancing the flexural and shear performance of deficient bridge columns. In this paper, an analytical model is developed for the first‐yield limit state and the ultimate limit state of flexurally dominated steel‐jacketed circular bridge columns. Lateral stiffening of column is taken into account by considering the effective bond transfer between the steel jacket and column. Two possible ultimate limit states are identified: (1) A limit state that corresponds to the ultimate compressive strain of concrete; and (2) a limit state that corresponds to low‐cycle fatigue fracture of the longitudinal steel. An equation based on the energy balance method is proposed for predicting the ultimate compressive strain of concrete confined by the steel jacket. The ultimate limit state governed by low‐cycle fatigue fracture of the longitudinal steel is assessed using an energy‐based damage model. The proposed model is shown to correlate well with the lateral response of tested steel‐jacketed columns.

The paper reviews experimental evidence on the size effect caused by energy release due to fracture growth during brittle failures of concrete structures. The experimental evidence has by now become quite extensive. The size effect is verified for diagonal shear failure and torsional failure of longitudinally reinforced beams without stirrups, punching shear failure of slabs, pull‐out failures of deformed bars and of headed anchors, failure of short and slender tied columns, double‐punch compression failure and for part of the range also the splitting failure of concrete cylinders in the Brazilian test. Although much of this experimental evidence has been obtained with smaller laboratory specimens and concrete of reduced aggregate size, some significant evidence now also exists for normal‐size structures made with normal‐size aggregate. There is also extensive and multifaceted theoretical support. A nonlocal finite element code based on the microplane model is shown to be capable of correctly simulating the existing experimental data on the size effect. More experimental data for large structures with normal‐size aggregate are needed to strengthen the existing verification and improve the calibration of the theory.

The computational models used for compression members in the nonlinear analysis of space trusses are classified by decreasing order of computational effort into finite‐segment, finite‐difference, and single‐member solutions. The common assumptions and derivations used with single‐member solutions are reviewed. A chronological review of the models is given indicating the contributions each has made. Single‐member solutions can often give results similar to those that use more computationally demanding methods. However, the success of a model at correlating with experimental behavior depends on the assumptions made. Single‐member solutions that include partial plasticity appear more accurate than those that assume full plasticity at midlength. It is observed that consideration also needs to be given to the relationship between the member and the structure to which the member is attached. Thus, internal snap‐through or dynamic jump can occur in the postbuckling regime of compression members in a relatively compliant adjacent structure.

Modified values for the shear bond strength and coefficient of friction in a Mohr‐Coulomb type of failure criterion for concrete block‐mortar joints in masonry are calculated using finite‐element analyses in which it is assumed that the state of stress in the joint is nonuniform. The failure loads used in these analyses are obtained from three laboratory specimens. It is shown that the shear failure in concrete block‐mortar joints in masonry can be conveniently described by a single expression that has some dependence on the modulii of elasticity of concrete blocks and joint mortar. The modified values of the parameters in a Mohr‐Coulomb equation are verified by their successful ability to estimate failure loads in two additional laboratory specimens.

Seismic design provisions estimate the maximum roof and story drifts occurring in major earthquakes by amplifying the drifts computed from elastic analysis at the prescribed design seismic force level with a deflection amplification factor $\left(\mathrm{DAF}\right)$. A comparison of several seismic design provisions indicated that the deflection amplification factor in both the UBC and NEHRP Recommended Provisions, being equal to ${\mathrm{3R}}_w/8$ and $C_d$, respectively, is very low and could lead to unconservative drift estimations. An analytical study of the seismic responses of four instrumented buildings confirmed that drifts developed in major earthquakes are much higher than those predicted by the UBC or NEHRP approach. It is recommended that the deflection amplification factor be increased to at least the seismic force reduction factor ($R_w$ in UBC and $R$ in NEHRP) for estimating maximum drifts. The effects of the ratio between building period and earthquake predominant period, types of yield mechanisms, and structural overstrength on the $\left(\mathrm{DAF}\right)$ are also presented.

The paper deals with a methodology for the use of dynamic response as an inspection and surveillance tool for concrete structures (mainly bridges). The method is based upon a finite‐element analysis for identification of stiffness characteristics (related to cracking) starting from modal dynamic parameters (natural frequencies and mode shapes) derived from dynamic tests. The use of dynamic data is convenient because acceleration transducers can be easily mounted in the structure instead of displacement transducers, mainly when the bridge to be tested overpasses a river, high valley, or traffic road. Several damage‐identification examples are performed with groups of reinforced concrete beams with different and well‐defined cracking patterns. Dynamic response is measured by acceleration transducers. This experimental verification clearly shows the effectiveness of the proposed method in the identification of location, extension, and amount of cracking when some important requirements concerning the dynamic data recorded are taken into account. In particular, more than the first natural frequency must be evaluated.

The paper describes a method of inelastic analysis for steel frames that provides the accuracy of distributed plasticity methods with the computational efficiency of elastic‐plastic‐hinge methods. It accounts for spread‐of‐plasticity effects without the need for through‐section and lengthwise discretization of a beam‐column element. This is accomplished through nonlinear equations for the force‐strain relationships of the cross section that are calibrated to data from inelastic analyses and numerical integration of the cross‐section model along the element length to obtain inelastic flexibility coefficients for the member. The flexibility coefficients are employed in generating an inelastic stiffness matrix in which geometric nonlinearity is also accounted for. The proposed model has been implemented and tested using several example problems known to be sensitive to spreading‐plasticity effects.

An experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions. Eight two‐thirds‐scale specimens were tested, each consisting of a structural steel shape encased in reinforced concrete. The parameters studied in the test program included the degree of concrete confinement required to achieve adequate ductility under cyclic loading, effectiveness of flange shear studs for enhancing flexural stiffness and strength, concrete compressive strength, and the shear resistance mechanism of the composite column. The results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited. The encased steel shape was found to provide the primary resistance to transverse shear during overloading, with the shear studs not effective in enhancing the flexural resistance to lateral loading. The specimen flexural capacity under combined axial and lateral loading was found to be accurately predicted by analytical models based on full composite action, with ACI and AISC LRFD criteria providing conservative results.

A wind‐tunnel study has been carried out to assess wind loads on multispan gable roofs with roof slopes of 4:12 and 12:12. Local and area‐averaged pressure coefficients were measured on models with one, two, and four spans. Critical suctions were significantly larger than those specified for single‐span roofs in wind standards. Discrepancies between single‐span design pressures and the multispan results were largest for the high‐pitch roof, for which local suctions obtained in the present study exceed the wind‐standard values by a factor of two. Suctions measured on the 4:12 single‐span and multispan roofs were 20–50% higher than design values specified in wind standards for single‐span buildings. Critical values of positive pressures measured on the 4:12 and 12:12 multispan gable roofs agree well with design pressures specified in wind standards for single‐span gable roofs. The largest positive pressures occurred on the high‐pitch roof along the low edge of the windward span and in the trough regions. The present paper proposes design pressure coefficients for multispan gable roofs.

The bond strength of welded wire fabric (WWF) in concrete bridge decks was investigated by testing 22 pullout specimens for bond strength up to their ultimate capacity. The pullout study showed that after the bond between longitudinal wires and concrete failed, the specimens resisted additional loads due to the anchorage effects of transverse wires and shear strength of welds. This increase in bond strength ranged from 16 to 771%, depending upon the type and arrangement of longitudinal and transverse wires. The transverse wires and shear strength of the weld, therefore, make large contributions to the bond strength of the welded wire fabric in concrete bridge decks.

The splicing strength of welded wire fabric (WWF) in concrete bridge decks was investigated by testing three one‐way slabs reinforced with spliced WWF, and one slab reinforced with WWF without a splice. The slabs were tested up to their ultimate capacity. The experiments showed that the specimens with transverse wires in the splice zone had an early separation of the spliced steel, thereby resulting in concrete cover failure. A new splice detail without transverse wires in the splice zone resulted in a gradual (more ductile) failure mode and a strain distribution similar to the slab without a splice. It was also determined that the orientation of transverse wires, distribution of longitudinal wires, and weld shear strength are the major factors affecting the splice strength of concrete bridge slabs reinforced with welded wire fabric.